The interplexiform cell has been the last major class of retinal neurons to be discovered. It provides long distance feedback from the inner retina to the outer retina, yet little is known about the function of this class of neuron. The interplexiform cell is the only neuron that provides glycinergic signals to the distal retina in amphibia. This provides an opportunity to explore its function. In this proposal, I will investigate how glycinergic interplexiform cells regulate the physiology of the distal retina. The overall hypothesis is that glycinergic interplexiform cells enhance the output of photoreceptors and the level of enhancement increases as the retina progresses from a dark to a light adapted state. The first aim will be to determine the mechanisms by which the glycinergic interplexiform cells increase photoreceptor transmitter release. The second aim is to evaluate the direct effect of glycinergic interplexiform cell on horizontal cells, and to discern the mechanism of action. The third specific aim is to contrast the physiology of the glycinergic interplexiform cell in the dark and the light adapted retina. The application will place an emphasis on how glycinergic interplexiform cells affect neurotransmitter release in rods and cones, and on the fundamental mechanisms of the glycinergic interplexiform cell in dark and light adapted states in terms of the effects on photoreceptor transmitter release and horizontal cell depolarization. This analysis will serve as a contrast to the dopamine system, another mediator of light adaptation. The results of this study should provide an improved appreciation of the role of the interplexiform cell and should also expand knowledge of the molecular events that occur during light adaptation.